Absorbent core



United States Patent [72] Inventor Gunnar Gravdahl [56] References CitedHashim, Norway UNITED STATES PATENTS No 123%?1968 1,974,578 9/1934Medoff 128/290 2,964,039 12/1960 Johnson, Jr., et a1 128/290 [451Patented 3 430 629 3/1969 Mu h 128/284 Assignee Saba s 113 y Tonsberg,Norway Primary Examinercharles F. Rosenbaum [32] Priority Feb. 8, 1967Attorney-Wenderoth, Lind and Ponack [33] Norway [31 No. 166,765

ABSTRACT: An absorbent, pillow-shaped core, intended for [54] Q use in asanitary napkin, a diaper, compresses or the like, rawmg made of fibrousmaterial, the fibrous material provided with [52] US. Cl 128/284,gradually varying mass density, such that a greater number of 161/124fibers per volume is present in the portion of the core having [51] Int.Cl A6lf 13/16 the greatest need for absorption power, the mass density[50] Field of Search 128/284, gradually reduced in direction away fromsaid portion, the

287, 290, 296; 16 l/l24 core having substantially the same thickness allover.

PATENTED on: 8 I970 GNNAR GR AVDAHL JNVENTOR.

ABSORBENT CORE This invention relates to fibrous, absorbent,pillow-shaped cores of the kind used in sanitary napkins, diapers,compresses etc.

The invention is particularly useful for disposable sanitary napkins andshall in the following be described and illustrated. The invention can,however, be utilized for a number of various absorbent articles of thekind which are to be used once only, i.e. diapers, compresses, as longas these articles comprise an absorbent pillow-shaped core, which isencompassed by some kind of a wrapper.

A disposable sanitary napkin consists usually of two main parts, namelythe absorbent core, which during use shall absorb and confine themoisture, and a wrapper which primarily keeps the core in place andcarrying same, and also serves the purpose of preventing that theabsorbed liquid leaves the napkin.

A sanitary napkin core is usually about to cm. long and 4 to 8 cm. wide.The secretion of the menstruation liquid takes place, however, in arelatively concentrated manner. The need for absorbing capacity orability is therefore far the greatest in the centre portion of thenapkin, since it is in this area the substantial part of the liquid notonly must be absorbed, but also must be confined. In order to reachoptimal utilization of the total absorbing capacity of the napkin it isof importance that the napkin is so constructed and shaped that themoisture or liquid is distributed also sideways or laterally, and thenpreferably in the longitudinal direction of the core.

When hitherto faced with the task to make a core having the greatestabsorbing' power or ability in the centre portion of the core, theindustry has provided a core, which viewed in side elevation presents asubstantially elliptical shape. Such a shape is sometimes advantageousand sometimes disadvantageous. In a sanitary napkin it will beadvantageous that the napkin has such a shape during use, since aflattened front portion on the napkin will be less revealing under fightclothes, and a flattened rear portion will be more comfortable when thewearer is sitting. An elliptical shape will, however, involvedisadvantages during the production stage and in connection with thefurther handling in factory, particularly in connection with'masspacking machinery. It is also difficult to make an attractive packedproduct when same has an uneven thickness, such as the before mentionedelliptically-shaped article, particularly if the wrapping material issoft and flexible, for instance a plastic material.

The object of the invention is to provide a new embodiment for suchcores, with improved absorbing characteristics and also possessing ashape which simplifies handling and packing and provides an attractiveproduct.

The invention is based on the concept of making the fibrouspillow-shaped core such that the fibre material is present in the corewith gradually varying mass quantity per unit volume in the core suchthat a greater number of fibres per volume constitutes the portion ofthe core having the greatest need for absorbent ability, the massquantity per volume decreasing gradually in all directions away fromsaid portion, the core having substantially the same thickness all over.A core in accordance with the invention will thus possess a systematicor predetermined gradually-varying mass-density distribution.

Within this inventive concept one can make cores having a wide varietyof characteristics, making it possible to suit any particular need andhaving the characteristics and qualities desired.

In connection with a core for a sanitary napkin the concept will involvethat the core mass is designed to have the greatest density in thecentre portion of the core, the density gradually decreasing to bothsides laterally outwardly and in longitudinal direction of the core,simultaneously as the cross-sectional area depth of the core can be madeto be substantially constant. Hereby is obtained that the absorbingcapacity is concentrated in the area where the need is greatest, i.e. inthe centre portion, since this portion will contain most mass pervolume. Simultaneously, however, a gradually reduced mass density toboth sides in longitudinal direction of the core will result in that theabsorbed liquid easily will be distributed from the centre of the core.The resistance against liquid penetration and thus the liquiddistribution ability of the core will (always) increase as the massdensity decreases. This property is efiectively utilized by theinvention such that conventional special distribution layers or the likecan be entirely omitted.

A core in accordance with the invention is suitably made by having thecore material, for instance defibrated cellulosis continuously producedin the shape of a web in per se known machinery having varying oralternating mass density in the longitudinal direction, the cycles orfrequency of the alternations corresponding to the desired length ofeach individual sanitary napkin core. Simultaneously the web is givenuniform or substantially uniform thickness and width, i.e. constantcross-sectional area per unit length. The web is thereafter cuttransversely through the portions having the least mass density intoindividual napkin cores.

In the following the invention shall be described in detail withreference to the accompanying drawing, where,

FIG. 1 shows a longitudinal sectional view through a core ofconventional type,

FIG. 2 shows a similar longitudinal sectional view through a sanitarynapkin core made in accordance with the present invention.

FIG. 3 shows the napkin core shown in FIG. 2, having the shape it willattain when the napkin wrapper is subject to tension and/or sidewayscompression.

The conventional napkin core 2, shown in FIG. 1, comprises severallayers 4, 4, etc. each having decreasing length viewed from the centreportion, such that the core in longitudinal sec tion (and possibly incross section) is attaining substantially elliptical shape, as indicatedwith dotted lines 6. One or more liquid distributing layers canbepositioned between the layers. In the FIG. is shown a distributinglayer 8 in the centre of the core.

A napkin core 10 in accordance with the invention is shown inlongitudinal section in FIG. 2. As it appears, the mass density-which isvisualized by the degree of the hatching-is vary- .ing, and it isgreatest in the centre. Furthermore, it will be observed that the core,seen in longitudinal section, has a rectangular shape. To what extentthe rectangular cross-sectional shape of the core will be retainedsubsequently (and provided with wrapping) will depend upon severalfactors, such as the flexibility of the material (i.e. the elasticity ofthe fibres), the mass density and the specific properties of thematerial. By treating the core with binding, adhesion or stiffeningcompositions one can eliminate or reduce the propensity of thematerialto return to the original shape and condition subsequent to acompression or squeezing together.

In most cases the core will possess, however, subsequent to its making,some inherent propensity to expand, the magnitude of this expansionforce will be somewhat proportional to the mass density, such that thecore may, if desired, sub sequent to its making immediately attain ashape which can be compared with the shape of the core shown in FIG. 1,but a core in accordance with the invention will still retain suchgreater mass density in the centre portion, such as illustrated in FIG.2.

When making cores for sanitary napkins it has proved advantageous, asmentioned before, to make the core such that the core has asubstantially rectangular shape, viewed in longitudinal section, amongother reasons because this shape facilitates the handling of the coreand the packing of the napkins, and which among other operationsinvolves that the mp respective ends are attached to a belt)particularly the end portions of the napkin core will be subject tocompression or sideways squeezing, such as schematically illustrated inFIG.

ing mass density from the centre the squeezing together of the endportions of a core in accordance with the invention will be much larger,and the compression forces K towards the end portions of the core alsowill result in a force component designated with the capital letter Fdirected towards the centre and thereby contribute to deliberation ofinherent expansion propensity of the fibres and the mass in the centreportion of the core, so that the centre portion in fact may tend toexpand. Tests have shown, however, that a napkin core in accordance withthe invention still will retain a much larger mass density in the centreportion, so that this portion possesses greater absorbing capacity andmaintain ability to distribute moisture and liquid to the surrounding,more porous material.

In that the end portions of .the napkin core are squeezed together-moreor less-during use, the napkin will thereby attain the desirouselliptical cross-sectional shape enhancing wearing comfort etc. Thenapkin core may nevertheless initially have a rectangularcross-sectional shape with the described advantages attained thereto.

By varying the mass density of the core, particularly the mass densityvariation in longitudinal direction, it has proved to be possible tomake napkin cores having just the absorbing and expanding qualitieswhich are desirable for the particular need in question.

Iclaim:

1. An absorbent core having substantially the same thickness throughoutbefore being used and not being subjected to external forces ofcompression, for use in a sanitary napkin, a diaper, compresses and thelike comprising a flat unitary, integral body of absorbent fibrousmaterial, said fibrous material in said body having a gradually varyingmass density so that a greater number of fibres per volume is present inthat portion of said body having the greatest need for absorbing power,said mass density being gradually reduced in a direction away from saidportion.

2. An absorbent core in accordance with claim 1 wherein said body whenexposed to substantially evenly distributed compressional forces againstthe side face areas thereof attains a substantially oval shape in alongitudinal cross section 3. An absorbent core in accordance with claim1 wherein said body is resilient.

